Press system



T. F. STACY March 2, 1937.

PRESS SYSTEM i'i-led May is, 1953 2 Sheets-Sheet 1 WQM March 2, 1937. T.F. STACY 2,072,141

PRESS SYSTEM Filed May 15, 1933 2 Sheets-Sheet 2 fi/ (7 a! if 55'- /fii1% J Jif 61f" AZY'WJ.

?atented Mar. 2, 1937 UNITED STATES PRESS SYSTEM Thomas F. Stacy, Piqua,Ohio, assignor to The French Oil Mill Machinery (30., Piqua, OhioApplication May 15, 1933, Serial No. 671,197

27 Claims.

This invention relates to press systems and particularly to an improvedmanner of controlling the operations of a press. An object of theinvention is to provide an improved system for hydraulic presses and thelike, by which the operations of the press may be carried out more orless automatically, and which will be extremely simple, dependable, andinexpensive.

Another object of the invention is to provide an improved system forhydraulic presses and the like, in which changes in the operation of thepress may be established quickly; with which the operation of the presswill be rapid; with which there will be a maximum number ofsafeguards-against injury to the operators, and with which the powerstroke of the press may be continued for any selected and predeterminedinterval of time after the platen passes a selected point in its traveland then automatically stopped.

Another object of the invention is to provide an improved controllingsystem for hydraulic presses and the like with which the operator musthave both hands out of dangerous positions with respect to the pressbefore the press can be started; with which the operation of the platenmay be stopped and held in stopped position, or reversed quickly at anypoint in its forward or pressing movement, and with which the platen maybe held in any position under a selected pressure.

Various other objects and advantages will be apparent from the followingdescription of an embodiment of the invention, and the novel featureswill be particularly pointed-out hereinafter in connection with theappended claims.

In the accompanying drawings, Fig. 1 is an elevation, partly in section,of a hydraulic press constructed in accordance with this invention, andhaving associated therewith a controlling system which is illustrateddiagrammatically;'

Fig. 2 is a sectional elevation, partially diagrammatic, of a simpleform of a time limit relay;

Fig. 3 is an elevation of a portion of the press of Fig. l, and adiagram of the control apparatus which is associated therewith andillustrating another embodiment of the invention by which a fullautomatic operation of the press may be obtained with a time dwell atthe open position; and

Fig. 4 is a view similar to Fig. 3 except that the control device doesnot start an opening movement of the platen until the pressure in themain ram has reached a predetermined pressure.

In the embodiment oi. the invention illustrated in Figs. 1 and 2, thepress is hydraulic and includes a base i, and a platen 2 which ismounted for reciprocation ton upright posts 2, The platen 2 is moveddownwardly toward the base I by ,a

main ram formed of a plunger or pistonl which reciprocates in a cylinder5, the piston 4 being connected at its lower end to the platen 2. Rods 6carried by the platen 2 extend upwardly therefrom and at their upperends are connected by a yoke l which, in turn, is connected to a rod orpiston 8 which reciprocates through one end of a cylinder 9. The piston8 and cylinder 9, together, form a pull back ram which, operatingthrough the yoke i and rods 6, serves to lift the platen 2 when fluidunder pressure is admitted to the cylinder 9.

A reversible pump l0, which preferably .is of variable delivery, isconnected at one side by a pipe II to the cylinder 5 of the main ram,

I and at its other side by a pipe 12 to the cylinder 9. The pipe i2between the pump and the cylinder 9 includes a free check valve i3 whichautomatically opens to'permit flow of fluid from the pump through thepipe l2 to the cylinder 9 and automatically closes to prevent reverseflow. The pipe l2, between the pump i and the valve I3, is connected bya pipe it to another check valve i which, 'in turn, is connected by apipe [6 to a source I! of a fluid under pressure. Since the fluids insuch presses are usually liquid, the source of fluid may be a closedtank having an air chamber at the upper part thereof and otherwisefilled with theoperating liquid.

A pipe l8 opens into the lower part of the tank I! and carries a valvel9 which, in the normal operation of the press, is always open,

but constitutes atankshut off valve which may be operated during repairsto the press. The pipe I 8, after passing the valve I9, opens into adifferential check valve 20. This differential check valve 20 has acentral or intermediate chamber 2| which opens into an'end chamber 22through an apertured seat 23, and-also opens into an opposite endchamber 24 through an apertured seat 25. A valve stem 26 extends throughboth the end chambers and the central chamber, and within the endchamber 22 carries the valve element 21' which'moves within that endchamber into and out of closing or seating position on the seat 23 uponreciprocation of the stem 26.

A valve element 28 abuts, but is separate from, the lower end of thestem 26 and moves back and forth in the other end chamber 24 into andout of engagement with the seat 25 whereby communication between thecentral chamber 2| and the end chamber 24 is broken or established bythe position 01 valve element 28. A spring 28a urges the valve element28 into closed position on seat 25. Since the valve elements 21 and 28are on opposite sides or the two valve seats 22 and 25, it followsthatwhen thevalve element 21 opens, the element 28 may or may not close,

and when valve element 28 closes, the element 21 must open.

It will thus be seen that the pipe l8 will conduct the operating liquidfrom the tank H to the central chamber 2| of the difierential checkvalve 28, and from the chamber 2| the liquid will pass into one endchamber or the other, depending upon the relative positions of thevalveelements 21 and 28. The valve stem 26 extends upwardly through theend chamber 22 and into a piston chamber 29,- the passage from the endchamber 22 into the piston chamber 29 being provided with a suitablepacking gland 38. The stem 26 at its end within the piston chamber 29carries a piston or head 3| which reciprocates back and forth in thechamber 29 with the stem 26. i i

The piston 3| is forcibly reciprocated in the chamber 29 by an operatingfluid, such as compressed air, the source of which is indicated by acompressed air tank 32." A pipe 33 connects the air tank 32 to thechamber of a valve box 34, and from this valve box pipes 35 and 36 leadto opposite ends of the chamber 29 and at opposite faces of the piston3|. A reciprocating valve element is provided inthe box 34 to controlthe admission of fluid from the valve box alternately through the pipes35 and 36 to opposite ends of the cylinder 29. For this purpose, thepipes 35 and 36 open into the chamber of the .valve box 34 throughsuitable ports arranged along the path of travel of a reciprocatingvalve element 31 and, in addition, an exhaust port 38 also opens intothe valve box through a suitable port between the ports of the pipes 35and 36.

When the valve element 31 is in the position valve shown by full linesin Fig. 1, the chamber 39 in the face thereof which moves across theports of-the valve pipes will be in a position to establishcommunication between the exhaust pipe 38 and the pipe 36 which leads tothe lower end of the chamber 29. At this time the port of the pipe 35will be uncovered by the valve element 31 and, consequently, compressedair from the pipe 33 will pass through the valve box and pipe 35 intothe upper end of the chamber 29 and force the piston 3| downwardly intothe position shown in Fig. 1 and will hold it in that position.

If the valve element 31 is moved upwardly, it will uncover the port ofthe pipe 36 and will connect the port of the pipe 35 with the port ofthe exhaust pipe 38. This position is shown by dash lines in thedrawings and when the valve is in this position, the upper end of thechamber 29 will be connected to atmosphere through the exhaust pipe 38and the compressed air from the pipe 33 will pass through the pipe 36-tothe lower end of the chamber 29 so asto force the piston 3| upwardly andthus move the valve element 21 away from its'seat, and concomitantlyrelease the valve element 28 for possible movement into closed positionon its seat. Thus, by operating the valve element 31 one may cause anoperation of the differential check valve to establish communicationbetween the tank l1 and the two rams alternately or concomitantly. Thedelivery oi the pump l8 may be reversed by reciprocation oi a controlrod 48 which extends into the chamber of a cylinder 4| and, withinthe'cylinder 4|, carries a piston or head 42. Another valve 50:: 4-8,

similar to the box .34, is provided to controi the operation of thepiston or head 42, and for this purpose pipes 44 and 45 extend from theopposite ends of the cylinder 4| to the valve box 43 and open into thechamber of the valve box through suitable ports, the same asin the box34. This box also has anexhaust pipe 46, and a pipe 41' connects thepipe 33, leading from the compressed 7 air tank 32, to the chamber ofthe valve box 43.

pipe 46 alternately with the ports leading to the pipes 44 and 45. Byshifting thevalve element 48 in the box 43, the compressed air may beadmitted alternately to the opposite ends of the cylinder 4| whichcauses reciprocation of the piston or head 42 in alternate directions toreverse the delivery of the pump |8. By reversing the delivery of thepump, the operating fluid or liquid may be transferred alternatelybetween said rams and, thereby, the platen 2 may be moved in eitherdirection. z

' The check valve l5 also serves as a by-pass valve, and for this p p seits valve element 58 is mounted for free movement toward and from itsseat 5|, so as to close automatically and pre vent flow of an operatingfiuid from the pipe |4 into the pipe I6, yet open automatically andpermit a reverse flow from the pipe Hi to the pipe I4. The valve element58 abuts endwise against an operating stem 52 which depends through a.

packing gland 53 and terminates in a head 54. A

spring 55 acting between the head 54 and the packing gland 53 yieldinglyurges the stem 52 away from valve element 58 to allow element 50 toengage its seat'5l.

An operating rod 56 is guidedin a'suitable bearing 51 on the basel andin a depending bracket 56A of the casing of the valve l5, so as toreciprocate endwise against the head 54. The rod' 56 is limited in itsdownward movement by v the engagement of a head on its upper end withthe bracket 56A. The platen 2 is provided with an arm '58 which isadapted, as the platen 2 approaches its desired upward limited travel,to engage with a collar 59 adjustably carried by the rod 56. Thus, asthe platen 2 approaches a selected point in its upward travel, itengages the collar 59 and through it' lifts the rod 56 and stem 52 andcams the valve element 58 into open position for a purpose which willappear as the description proceeds. When the platen 2 starts downwardlyagain, it will release the collar 59 and the spring 55 assisted bygravity will move the rod '56 and stem 52 downwardly and release thevalve element 58 which is then free to move into closed position.Various means may be employed for operating the valve box elements 31and 48 to control the operations of the press, but in the drawings Ihave illustrated an electrical system of control which I find tobesatisfactory. With such a system the valve element 31 is operated by astem 68 which extends. outwardly of the box and is operated by asuitable solenoid 6|. Similarly,

- a rod 62 is connected to the valve element 48 of 61 connects the powerline Ll to one side of the solenoid. 63 which controls the reversal ofthe pump, and the other side of that solenoid is connected by a wire 68to a contact 69. The contact 69 is connected by a switch bridge 18 to acontact II, which in turn is connected by a win '2 to the other powerline L2. The switch bridge I8 is carried by and insulated from a stem 13which is connected to the core 14 of a solenoid which functions as amain 'relay. One end or side of the relay or solenoid I5 is connected tothe wire 61 and through it to the power line LI, and the otherside ofthe relay or solenoid I5 is connected by a wire 16 to the other powerline L2. A pair of switches H are included in series with one anotherand with the wire I6, so that the circuit through the main relay I5 canonly be closed by the closing of both switches H. type which areresiliently urged into open po sition, and together the two switchesjointly control the main relay.

A holding or stick circuit for the main relay is provided for keepingthe relay energized after the main relay circuit is closed, and for thispurpose a bridge 78 is also carried by the stem I3 so as to bridgecontacts I9 and 88. The contact 88 is connected by a wire 8I to one ofthe power wires, such as L2, and the other'contact I9 is connected by awire 82 to one side of a switch 83 which is yieldingly urged into aclosed position by a spring 84.

The other side of the switch 83 is connected by a wire 85 to one side ofan emergency return switch 88 which is yieldingly urged into closedposition by a spring 81. The-other side of the switch 86 is connected bya wire 88 to the wire l6 at a point between the switches TI and therelay 15. This stick circuit may, therefore, be traced as follows:Fromthe power line LI, through wire 61, relay solenoid I5, wires '56 and 88,switch 86, wire 85, switch 83, wire 82, contact l9, bridge 58, contact88 and wire 8I back to the other power line L2. It will thus be seenthat this stick circuit is closed and opened by a bridge 18 which isoperated by the relay when the relay is energized, and this circuit isalso controlled by the normally closed switches 83 and 86.

One side of the solenoid winding 6| which controls the operation of thediflerentialvalve is connected by wire 89 to one of the power lines,such as LI, andv the other side of the winding is connected by wire 98to a contact 9|. The contact 9| is connected at intervals by a bridge 92to a contact 93 which, in turn, is connected by a wire 94 to the otherpower line L2. From this it will be observed that the solenoid winding8| is connected to the power lines by the bridge 92 and this bridgeforms part of an auxiliary relay 95. The winding of the relay 95 isconnected at one side to the wire 89 which leads to the power line LI,and at its other side is connected by a wire 96 to a switch 91.

The other side of the switch 91 is connected by a wire 98 to a contact99 which is connected at intervals by a bridge N8 to the contact III!that, in turn, is connected by a wire I82 to the other power line L2.Thus. when the main relay I5 is energized, the bridge I88, which iscarried by the stem 13 of the relay I5, is shifted into bridgingrelation with the contacts 99 and I8I,- thereby closing the circuitthrough the switch 91 and the auxiliary relay 95, which closing of thiscircuit, in turn, through the operation of this relay 95, closes thecircuit of the solenoid The switches are of any suitable GI whichcontrolsthe operation of the differential check valve.

The switch 91 may be shifted into open position against a neutral postI83, and a spring I84 acting on the switch 9'! holds the switch ineither open or closed positions yieldingly, owing to the fact that thespring I84 passes a dead center position while moving in eitherdirectionbetween open and closed positions. The switch 91 may be designated as amaintaining contact switch, and its function will appear as thedescription proceeds.

A suitable timing device is associated with the switch 83 which controlsthe stick circuit of the main relay, and, is intended to open this stickcircuit a predetermined and selected or adjustable interval of timeafter the platen has been started on the pressing stroke by the mainram. Such a timing device may be of any suitable type of which there aremany on the market, including electric motors operating suitable camsthrough gear trains, such as are commonly employed in trafiic signals,for example, or suitable clock mechanisms or time limit relays may beemployed. In this particular example, for simplicity, a time limit relayhas been illustrated and is shown diagrammatically in Fig. 1 and des-"ignated by the reference character I85.

The winding of this relay I85 is connected across the lines 89 and 98which lead to the solenoid BI which controls the operation of thediiferential check valve and, therefore, whenever the auxiliary relay 95is closed through operation of the main relay I5, current will besupplied to the time limit relay at the same time that it is supplied tothe solenoid'BI to effect a change in the position of the differentialcheck valve. This time limit relay is arranged to engage and open theswitch 83 automatically a, selected and adjustable, predetermined lengthof time after current is supplied to the relay, and upon the opening ofthe stick circuit, the main relay I5 is automatically deenergized. Sincethe time limit relay is energized only whilethe main relay 15 isenergized, it follows that when the stick circuit is opened, the timelimit relay also will be deenergized and will return to normal position.

Any suitable form of time limit relay may be employed but one is shownmore or less diagrammatically on a larger scale in Fig. 2 and mayinclude a winding I86, a magnetically attractable core I81 carrying apiston I88 which reciprocates in a cylinder I89 to form therewith a dashpot. When the winding I88 is energized, it lifts the core I81 with itspiston I88 and the rate of this upward travel is controlled by theentrance of air through an adjustable valve II8 into the cylinder I89,inthe bottom thereof, that is, below the piston I88. When the pistonI88, however, has nearly reached the position where it operates theswitch 83, it uncovers a port III in the side of the cylinder I89, whichrelieves the partial vacuum created in the bottom part of the cylinder'I89 by the upward movement of the piston I88, and the core 181 maythenpass upwardly quickly and through a stem II2 thereof will engage andopen the switch 83, thereby preventing arcing of the contacts of theswitch.

' Following opening of the switch 83 of the stick circuit, the windingI88 will be deenergized, as explained herein above, and thereupon thecore I81 with-v its piston I88 will descend through the action ofgravity, or through the assistance of one or more springs H8, which actupon a cross arm I carried by the stem II2. A check valve H controls anair escape passage leading from the bottom part of the cylinder I09, sothat the air displaced by the downward movement of the V piston I08 mayfreely escape, yet when the pis- 5 ton I08 moves upwardly, the ballvalve H5 will automatically close and compel all the air to enter thecylinder I09 through the adjustable valve IIO. By adjusting the valveIIO, the rate of travel of. the piston I08 may be regulated, and thus.the time interval following energization of the main relay before thestick circuit is opened may be regulated. The upper end of the stem II2may be guided by rods I I6 which have sliding engagement with the crosshead H4. It frequently happens that full automatic operation ofthe-press is desired and, accordingly, I have provided means forreversing the press automatically when it reaches open position. In theillustrated example for accomplishing this result, and referring to Fig.1 of the drawings, a normally open switch II 1 is provided on the frameor base 3 of the press in a position to be opened automatically by theplaten when it reaches open position. Since the platen does not alwaysoccupy the same open position and since the open position is determinedby the position of the collar 59 on the rod 56, I have provided anothercollar I I8 on the rod 55, the collar II8 being secured in the properposition on the rod 56 by aset screw or other suitable means. The collarhis set to engage and close the switch III automatically when the rod 56is elevated through engagement of the arm 58 of the platen 2 with thecollar 58, because the open position of the platen is determined by theraising of the A wire H9 is connected to the wire I8, which Is connectedto one side of the double starting I switch 11, and is also connected toone terminal or contact of the switch III. A wire I20 is connected tothe other terminal or contact of the switch Ill and to a switch I2Iwhich is yieldingly held in either of two positions, one of which is aclosed position and the other of which is an open position. This switchisshown in closed position by full lines in Fig. 1 and in open positionby dash lines in the same figure. The switch is similar to the switch91, and the spring I22, which is connected thereto, in passing deadcenter or the pivot of the switch I2I, yieldingly urges the switch ineither position. The switch I2I is infrequently operated and hence ispreferably so located as to be less accessible than the dual con trolswitches II. It also may be so disposed that this operator must removehis hands from the work in order to reach it. It also may be placedanywhere and locked in either position so that the control of the pressoperations is normally in the switches ll. A wire I23 connects the other0 terminal of the switch I2I with the wire 8I which leads immediately tothe power line L2 which is, in eifect, connecting the wire I23 to theother side of -the double switch II.

From this arrangement it will be observed that the switch I" isconnected in parallel to the double switch I1, and that the closing ofthe switch I" will perform the same function as the double switch 71.Thus, as the platen 2 reaches its upper or open position, as determinedby the adjustable collar 59, it lifts the rod 56 and closes the switchII! which closes a shunt circuitaround the double switch 11 andinitiates a reversal of the travel of the platen. When the platen startsdownwardly again, the rod 56 will 75 i' mediately be released and willdescend. thus releasing the switch II! which automatically moves intoopen position, due to the resiliency of the contacts thereof.

If one desires to eliminate the automatic reversal of the platen when itreaches open or upper position, then one moves the switch I2I tothe'open position shown by dash lines in Fig. 1 whereupon the shuntcircuit around the double switch ll will be broken, and the closing ofthe switch I "by the platen will no longer cause a reversal of thedirection of travel of the platen. It will be necessary then to closeboth switches TI in order to start a downward movement of the platen.

The operation .of the system which has been illustrated will now bedescribed. With the parts in the position shown in Fig. 1, the press isidle with the platen 2 elevated. At this time the pump I0 is deliveringoperating liquid'through the pipe I2 to the pull back ram, but since theby-pass check valve, at this time, is in open position, the deliveredliquid will pass through the pipes I4 and I6 back into the tank I1, andfrom the tank I! it will flow through the pipe I8 and the differentialvalve into the main ram cylinder 5 and thence through the pipe I I tothe intake side of the pump. At this time, the check valve I3 is closedbecause the pressure in the pull back ram cylinder 9 will be greaterthan that delivered by the pump, and since the valve element 21 is inclosed position, the pressure in the pull back cylinder 9 will hold theplaten 2 in its upper position.

If now one desires to cause a descent of the platen 2,'such as in apressing operation, the attendant or operator operates both ofthe starting switches 11 simultaneously, because both of these switches must beclosed at "the same time in order to establish a circuit through themain relay 15. By having two separate switches I1,

it will be necessary for the operator to use both,

hands to operate both switches at the same time before the press can be.started, and this is an important safety feature in that the operatormust positively have both hands free of the press in order to start adownward or pressing move ment of the platen.

A momentary closing of the switches 71 is all that is required becauseimmediately upon the closing of the circuit of the main relay IS, theupward movement of the stem 13 of that relay, which immediatelyfollows,,causes a closing of three circuits through movement of thebridges 18, I0 and I00. The closing of'the bridge 18 immediately closesthe stick circuit which thereupon holds the main relay l5 energized,regardless of the immediate opening of the switches I1, since the latterare immediately-returned to open position by their springs. At the sametime that the relay I5 is energized, the bridge I0, which is operated,closes the circuit through the solenoid 63, and this solenoid, byattracting its core 65, shifts the valve element 48 of the valve box 43time, the main relay I5, through the closingmovement of the bridge I00,closes the circuit through the auxiliary relay 95, and this relay 85 inturn operates the bridge 82 to close the circuit upwardly into thedotted line position shown in to the time limit relay and the solenoid6!. The solenoid 6 I, when energized in this manner, shifts the valveelement 31 into the dotted line position shown in the drawings and, indoing so, it con- 5 nects the compressed air from the tank 32 to thepipe 36 which conducts it to the underside of the piston 3| of thedifferential valve.

This compressed air acting on the under side of the piston 3| forces thedifferential valve stem 1 25 upwardly or outwardly and, in doing so,moves the valve element 21 away from its seat, at the same timereleasing the valve element 28 which is elevated upwardly into closedposition on its seat 25 by its spring 28a. Since the liquid in the 15tank H is under pressure, because the liquid from the main cylinder hasbeen displaced into the tank I! during the upward movement of theplaten, and the air in the chamber in the top of the tank I i has beencompressed, this liquid from the tank 11, which is under considerablepneumatic pressure, may now pass through the differential check valveinto the pull back ram cylinder 9 and also is sufiicient to overcome thespring 28a and open the valve element 28 and flow into the main ramcylinder. The pressure in this cylinder 5 forces the platen 2 downwardlyat a rapid rate,

and the liquid displaced by the pull back ram escapes through valve seat23 into passage 25. f

2 At the same time, the pump i d is drawing liquid I5, and the pipes I land I2, and delivers it through the pipe H to the main ram cylinder 5. Arapid movement of the platen 2 results because of the pressure createdthrough the liquid delivered by both the pump and also the tank ll.

As soon as the platen 2 encounters resistance to such an extent that thepressure required to cause further movement of the platen approximatelyequals the pressure then existing in the tank ll,

40 the liquid will no longer flow from the tank ll directly into themain cylinder 5, because the pressure is approximately equal in bothtank and ram cylinder, and thereupon the valve 28 will be closed by itsspring 28a.

45 The operating liquid will then move from the tank ll through the pipeIt, the valve 15, the pipes l4 and I2, through the pump, and thencethrough the pipe H to the main cylinder 5. When the platen 2 starteddownwardly, it re- 50 leased the collar 59, and the rod 56 then dropped,but the valve element 50 remained open owing to the suction through thepipes l2 and i 3 created by the pump, and the liquid passing through thepipe l6 holds the valve element 55 lifted. The

55 continued operation of the pump l0 will cause the gradual building upof pressure in the Ljlilldel 5 and an increasing pressure onthe platen2.

The pump [0 is of a well known reversible and variable delivery type andautomatically sets 60 itself to'neutral, or only sufficient delivery tooffset leakage, when the pressure in the delivery side to the main ramreaches a selected, but adjustable, maximum pressure. This may beaccomplished, for example, by connecting a branch pipe 65 a to the pipeH, and to a small cylinder b. A piston or ram 0 reciprocating in thecylinder b is connected to a pair of control levers d to operate them toneutral delivery position against the action of a spring 6 that reactsbetween an 70 adjustable abutment f upon the control rod 45 and a yoke gconnecting the control levers d.

The rod fill passes freely through theyoke g and terminates in a head40a so that the levers 01 may be positively moved to reverse the pumpand cause an operation of the pull back ram and a from the tank l1,through the pipe Hi, the valve return of the platen. When the rod 40 isshifted to the left (Fig. 1) by operation of the piston 42, the spring eis compressed and forces the levers d yieldingly into positions in whichthe pump delivers to the main ram. By adjusting the abutment f toincrease the pressure on the spring e, the greater will be the pressurerequired on the main ram, before the control levers d are shifted toapproximately neutral delivery position.

At the same time that the downward moveinent of the platen 2 wasinitiated by the closing of the main relay [5, the time limit relay orother .timing device was rendered efiective and a predeterminedand'adjustable length of time thereafter it opened the switch 83 of thestick circuit and caused a deenergization of the relay '15.

' Thereupon the bridges l8, l0 and I00 all moved into open position andbroke the stick circuit at another point and opened the circuitscontrolling the solenoids 6! and 63. Thereupon the springs 56 andgravity operate the valve elements 31 and 48 of the valve boxes back tothe full line positions and, in doing so, the compressed air is shut offfrom the pipes 36 and 45 and admitted to the pipes 35 and 45.

At the same time that the pipes 36 and 44 are connected to exhaust, so'that there will be no back pressure on the pistons 3i and 42. Compressedair is admitted to the pipes 35 and 45 and causes movement of the piston42 to the right and reverses the delivery of pump l0. Thereupon the pumpill draws liquid from the main cylinder 5, through the pipe H, anddelivers it through the pipe l2 and the valve iii to the pullbackcylinder 9, through the valve cavity 22, the valvecavity 2i, and backinto the tank H. In this manner the pressure in the press cylinder isdropped tozero. At the same time that compressed air is admitted to movethe piston 52 it is admitted to operate piston 38 of the differentialvalve into the full line position shown in the drawings. As soon as thepump has dropped the pressure by pumping out of the main cylinder, thelarge valve 28 with the pressure removed from its face is free to open.The piston 3| then forces the valve element 21 into closed position andthe stem 26 forces the valve element 28 into open position.

At this time the valve element 50 of the bypass valve !5 closesautomatically so as to prevent flow from the pipe M into the pipe E6.The check valve l5 opens freely at this time and the liquid delivered tothe pull back cylinder 9 will force the pull back piston or ram 8upwardly and lift the platen 2 Since the liquid displaced by the .mainram or piston 5 is greater than that necessary to supply the pump fordelivery to the pull back cylinder, the excess liquid in the maincylinder 5 will pass directly through the valve seat 25 and thedifferential valve chamber 2!, into the pipe i8, thence back into thetank ll, where the air in the tank I? is compressed and a new initialoperating pressure built up.

The return movement of the platen 2 is, there fore, relatively rapid.When the platen approaches the desired upward limit of its travel, thearm 58 of the platen engages the collar 59 which has been adjusted intoa selected position, and as the platen 2 moves further, the rod 56 islifted and the stem 52 elevated to force the check valve element 50 ofthe by-pass valve i5 into open position. Thereupon, the delivery of thepump to the pipe l2, insteadof passing into the pull back ram, will takethe path of least resistance through the pipe l4, valve I5, and pipe [6,to the tank l1, and since the check valve l3 will then ref to explain amo'diflcationin/the details of the It will be noted that current isconsumed for the electrical devices only when the platen is movingdownwardly in a. pressing direction, and none will be used while thepress is in idle position, as shown in thedrawings. If, for any reason,it is desired to stop the downward movement of the platen after adownward movement has been started and before. it has been completed,this may be done by manually opening the emergency return switch 86whichbreaks the stick circuit and causes an immediate return movement ofthe platen, the same as would be caused by the opening of the switch 83.a

If one desires to stop the press at any point in the downward movementof the platen and hold the platen in that position, the switch 91 ismoved into open position, shown by the dash lines in Fig. 1, at thedesired point in the downward movement of-the platen 2. When thishappens, the auxiliary relay 95 willbe deenergized, and this opens thecircuits to the solenoid BI and the time limit relay or timing deviceI95. The current will continue indefinitely to the solenoid 63 becausethere is now nothing to break the stick'circuit until the manual switch86 is opened, or the switch 9'I isreturned to closed position. When theauxiliary relay 95 opens the circuit controlled thereby, the valveelement 31 in thevalve box will returnto the full line position in thedrawmas and will reverse the diiferential valve. This causes a closing01' the valve element 2.1 on its seat and a forced opening 01' the valveelement 28. I

Since the delivery of the pump was not changed, it will continue todeliver the operating liquid to the main cylinder 5 but since thedifferential valve element 28 was opened, the operating liquid willtravel through the cylinder 5 and back to the tank in an idle circuit,so, that no further downward movement of the platen will occur becauseoil in the pull back ram can not escape. No upward or-return movementcan occur until the pump is reversed and, therefore, the platen 2 willremain in this position in which it is stopped until the switch 86 isopened or the switch 91 is closed. The switch 91 thus may properly becalled a maintaining switch because, by opening it, the press ismaintained or held in any position it may bein during. a pressingmovement.

In the'foregoing statement of the operation, it has been assumed thatthe switch I2I ie in open position, and that there has been no automaticreversal of the press as the .platen reaches open position. If now onedesires to have automatic operation of the press, the switch I2I ismoved into closed position, shown by full lines in Fig. l,

and thereupon whenever the platen reaches open position, and which openposition may varyas determined by the adjustment of the collar 59 on therod 56, the closing of the switch I IIupon the elevation of rod 56 willautomatically reverse the press and start a new downward movement in thesame manner that the platen would be started downwardly by an operationof the double switch II. This automatic reversal at open position can beeliminatedat any time merelyby shifting switeh' I2I back into. openposition, i:

Referring-next. to Fig. 3, the press is the same constructionas shown inFig. 1, but-only ,a fragmentary portion of it is illustrated in ordercontrol thereof. In Fig. 3 parts'periorming the same functions as inFig. 1 have been given the same reference characters, and will notbe'further described in detail. The control system shown in this Fig. 3is the same as in Fig. 1. except that a switch I24 is provided and isconnected by wires I25 and I26 to opposite sides of the double switch11. For example, wire I26 is connected to the wire 88 or the wire I6,and the wire I25 is connected to the power line L2 or to the wire whichconnects the power line L2 to one side of the double switch 11. Theswitch I24 is normally held in open position by a spring I2'I.

A time limit relay I28 is disposed in a position to close the switch I24when the relay is energized, and the coil or solenoid I29 of this'timelimit relay I 28 is connected at one side by wire.

I30 to the power line L2, and at the other side is connected to the wireI23 instead of having the wire I23 connected to the power line L2. Inother words, this arrangement is exactlythe same as in Fig. 1 exceptthat the switch I25 has-been added and the time limit relay I28 has beenplaced in series in the wire I23, so-thatwhen the reversing circuit,which isrendered operative by the platen as it reaches open position, isenergized, it will energize the time limit relay I28 and after the lapseof a selected and adjustable period of time, the switch I24 will beclosed automatically and a downward movement oi! the platen started aselected and predetermined interval or time after the platen has reachedits open position. This provides for a brief period of rest for theplaten-in its open position, and this period of time may be varied byadjusting the time limit relay to vary the period of time which willelapse after the relay is energized before the switch I24 is closed byit. This time limit relay' the voltage in that common circuit is dividedbetween the windings of both relays I5 and I29,

its lifting power. ,Sinoe relay I5 must operate against-a fixed ordefinite load, it is so designed that when subjected to a current atsuch a reduced voltage it will not be operated, but when full voltage isapplied, such as by closing switches 11, it will be operated. The relayI29 may, of course, be designed to operate at eitherthe reduced or fullvoltage. The operation or the control system shown in Fig. 3 isotherwise the same as describedfor Fig. .1.

In the embodiment of the invention shown in Fig.4, the arrangement ofthe control system is identical with that shown in Fig. 8, except thattheswitch 83 of the stick circuit for the main relay I5, instead ofbeing opened by the time limit relay I96, as in Figs. 1 and 3, aselected interval of time after the platen starts its downward orforward stroke, will be opened automatically after the pressure on themain ram 4 reaches a selected and adjustable, predetermined pressure. Toaccomplish this, the time limit relay I06 01 Fig. 3 is removed and inits place a pressure responsive mechanism is substituted. This *whichmeans that relay I5 has only a portion of mechanism includes a hydrauliccylinder I3I in lswitch 83.

A pipe I33 connects the interior of the cylinder I3I to the interior ofthe cylinder 5, and theredirectly responsive to the pressure in the maincylinder 5. As the pressure in the cylinder I3! increases, it will forcethe plunger I32 upwardly or outwardly and cause it to open the stickcircuit switch 83. The plunger I32 carries a yoke I34 and this yokeforms one end of a frame I35 which extends across the closed end of thecylinder and carries an adjustable abutment I36, between which and theend of the cylinder is disposed a compression spring I31. The upwardmovement of the plunger I32 is, therefore, resisted by the spring I31and, hence, the plunger I32 will not move upwardly and open the stickcircuit switch 83 until the pressure in the main cylinder has becomegreat enough, when transmitted to the cylinder I3I, to overcome theresistance of the spring I31. This resistance, which must be overcome,may be varied by adjusting the adjustable abutment I36, which mayinclude a screw threaded through the frame I35.

Thus, when the pressure in the main cylinder 5 of the press reaches apredetermined and selected pressure, the plunger I32 will open the stickcircuit switch 83, thereby deenergizing the main relay I5 and initiatingan upward or return movement of the platen. From this it will be seenthat the termination of the downward movement of the platen will beautomatically made after the pressure on the platen has reached aselected pressure, instead of a predetermined length of time after thedownward movement of the platen began, as in the device shown in Figs. 1and 3. Otherwise, the operation-is the same as in Figs. 1 and 3 andsimilar parts have corresponding characters.

In the system which has been hereinabove described, the timing relay ordevice I05, which automatically causes a reversal in the direction oftravel of the platen and initiates an upward movement thereof, begins tooperate at the beginning of the downward or pressing movement of theplaten. The speed of closing of the press is not always constant, forexample, varying with the temperature and consequent change in theviscosity of the oil and, therefore, it may at times be desirable tostart the timing device in operation at approximately the end of theclosing movement of the press and just before the real pressingoperation begins.

To make this possible, I may provide on the platen 2 an arm or controlfinger I38, Fig. 1, which is mounted on the platen for limited verticaladjustment such as by'making it slidable upon the vertical guide rod I39and securing it indifferent adjustable positions thereon by a set screwI40. The finger I38 thus moves with the platen 2 in both directions. Inthe path of travel of the finger I38, I mount a switch device I4I whichis closed by the finger I38 at various selected points in the downwardtravel of the platen, the switch remaining closed during the remainderof the downward travel of the platen. This switch is included in seriesin the circuit of the time limit relay winding I00.

Any suitable switch for this purpose may be employed but, byway ofexample, I have shown a lever or member pivotally mounted at I42 upon asuitable part of the press frame. The switch member has two arms I43 andI44. A spring I45 is connected to the switch member and to the frame ofthe press in a manner to pass dead center or the pivot I42 of the switchwhen the switch member is oscillated. A stop pin I46 limits theclockwise movement of the switch member so as to place the arm I43thereof in approximately a horizontal position in the path of travel ofthe finger I38. The spring I45 yieldingly holds the switch in thisposition.

When the finger I38 moves downwardly, it en gages the arm I43 and rocksthe switch member until the spring I45 passes dead center, whereuponthe' spring automatically snaps the switch further in the same directionuntil the arm I43 engagesa contact or switch terminal I41 suitablymounted onthe press frame. When the switch member is stopped in thisposition, the arm I 44 of the switch member is then above or behind andin the path of travel of, the finger I38 and the arm I43 is out of thepath of travel of the finger I38. The spring I45 holds the switch memberin this position. A wire I48 connects the wire 08 to the switch memberMI and a wire I49 connects the contact or terminal I41 to one side ofthe time limit relay I06, the other side of the time limit relay I08being connected to the wire 80.

With this arrangement, the winding I00 will not be energized when thesolenoid winding BI is energized, but when the platen 2 reaches aselected intermediate position in its movement in a pressing direction,it will rock the switch member I4I into closed position and leave it inthat position during the remainder of the downward or pressing movementof the platen. The time limit relay then functions and opens the stickcircuit a predetermined time after the platen passes the selectedintermediate position. When the stick circuit is opened in this manner,the mechanism sets the press controls to retract the platen 2 and, asthe platen 2 travels upwardly, the finger I38 will engage the arm I44 ofthe switch member I49 and will rock it until the spring I45 again passesdead center position. whereupon the spring will snap the switch memberinto the position shown in Fig. 1 in which the arm I43 is in the path oftravel of the finger I38 and the arm I44 is out of the path of travel ofthe finger I38. The circuit of relay I06 at the switch is operated tostart the functioning of the time limit relay may be adjusted or varied.Similar means for accomplishing the delay in the starting of the timingdevice may also be applied to the construction shown in Fig. 3.

It will be obvious that various changes in the details, which have beenherein described and illustrated in order to explain the nature of theinvention, may be made by those skilled in the art within the principleand scope of the invention, as expressed in the appended claims.

I claim:

1. In a hydraulic press system, a main ram, a pull back ram, a. platenoperated by said rams, a source of fluid, a reversible pump, connectionsbetween said rams, said source and said pump,

cause operation of said platen in either direction, and automatic meansfree of control by the pressure of fluid in either ram and renderedeffective by the platen as the platen leaves a predetermined adjustableposition during a pressing operation, for reversing said pump andcausing operation of said rams a selected interval of time thereafter.

2. In a hydraulic press system, a main ram, a pull back ram, a platenoperated by said rams ir alternate directions, a source of fluid, areversible pump, connections between said rams, said source and saidpumpand forming a hydraulic circuit by which fluid under pressure may bedelivered under pressure in either direction between said ramsselectively to cause opera tion of the platen in either direction,areservoir connected to said rams, a difierential valve having two checkvalve elements opening to pass fluid from 'said reservoir to each ramand automatically closing to prevent return flow, means i for operatingsaid valve and reversing said pump to cause a reversal in the directionof travel of said platen, and means free of the pressure upon a saidmain ram and also free of the speed of the operationiof said main ram,for automatically operating said reversing means and causing a returnoperation of said platen a selected interval of time after said platenpasses a selected and adjustable position in a pressing direction.

3. In a hydraulic press system, a main ram, a pull back rain, a platenoperated by said rams in alternate directions, a source of operatingfluid, pumping means, connections between said rams, said source andsaid means by which fluid may be delivered under pressure to said ramsselectively, electrical means for controlling the delivery of operatingfluid to one ram or the other and including a controlling circuit, andtiming means exclusive of the hydraulic circuit but set in operationautomatically when said electrical means is operated to initiate apressing, movement of said platen, and operable to cause a returnmovement of said platen atpredetermined length of time after thepressing movement of said platen is initiated.

.4. In a hydraulic press system, a platen, hydraulic rams connected tosaid platen to operate it in both directions, means including acontinuously operating pump connected to said rams for operating saidplaten in alternate directions depending upon which ram receives fluidfrom said pump, means for controlling the delivery of fluid to said ramsselectively so as to control the direction of operation of said platen,and a timing device exclusive of the pump but set in operationautomatically when said controlling means is operated to change thedelivery of fluid from said pumpfrom one of said rams to the other andcause movement of the platen in a pressing direction, for causing areversal of the platen a predetermined time after the desired movementof the platen in said pressing direction is ini-. tiated. v

" 5. In a-hydraulic press system, a platen, hydraulic rams connected tosaid platen to operate it in both directions, means including acontinuously operating pump connectedto said rams for operating saidplaten in alternate directions depending upon which ram receivesfluidirom said pump, means for controlling the delivery of fluid to saidrams selectively so as to control the direction of operation of saidplaten, and a tim ing device connected to said controlling means whilesaid platen is traveling in a pressing direction for changing thedelivery of fluid by said pump from one ram to the other and causing areversal of the direction of travel of the platen 'a predeterminedinterval of time thereafter, re-

gardless of the operating pressure upon, or rate of travel of, saidplaten.

6. In a hydraulic press system, a platen, means for operating saidplaten in alternate directions, means for controlling the direction ofoperation of said platen, a timing device exclusive of said operatingmeans, set in operation automatically when said controlling means isoperated to cause movement of the platen in one direction, for causing areversal of the platen a predetermined time after the desired movementof the platen in said one direction is initiated, and means forinterrupting theaction of said timing device and causing a return ofsaid platen selectively at any time, whereby in an emergency the returnof the platen may be accomplished before the expiration of saidpredetermined time.

7. In a hydraulic press system, a platen, hydraulic means for operatingsaid platen in alternate directions, a pump, means connecting said pumpand hydraulic means for causing operation of said platen in alternatedirections, a control device for controlling the delivery of said pumpto said hydraulic means for determining the direction of the operationof said platen, electrical means for controlling the activity of saidcontrol device, and means including said electrical means, a circuit anda relay for controlling the -activity of said electrical means so as tothereby control the operation of said platen, a stick circuit forsaidrelay, a time limit relay-operable on said stick circuit to open ita predetermined length of time after the closing of the first relay, anda circuit for said time limit relay controlled by the first mentionedrelay.

8. In a hydraulic press system; a platen, means,

relay, means including a timing device operable,

upon said stick circuit for opening it a predetermined interval of timeafter the energization of said relay and thereby causing a reversal inthe direction of operation of said platen.v

9. In a hydraulic press system,-a platen, means for operating saidplaten in alternate directions, means including a relay and its circuitfor controlling said operating means and having said circuit closed whenoperation of said platen in one direction is desired switch means forsaid relay circuit for closing it, a stick circuit for said relay, meansincluding a timing device operable upon said stick circuit for openingit a predetermined interval of time after the energization of said relaythereby causing a reversal in the direction of operation of said platen,and means operable separately from said stick circuit forstopping travelof said platen in a pressing direction, at any point insaid travel andholding it at that point at any time for emergency purposes,

10. In a hydraulic press system, a platen, rams operating said platen\in opposite directions,

'means including continuously operating pumpning means connected to saidrams fordelivering operating fluid to said'ramsalternately, and thusoperating said platen in alternate directions, a

source of operating fluid, connections from said source to both rams,valve means in said connections, a relay and its circuit, meanscontrolled by said relay for changing the delivery of said pumping meansfrom one ram to the other, means also controlled by saidrelay forchanging said valve means concurrently with the change in said pumpingmeans, switch means for closing said relay circuit to initiate anoperation of said platen in one direction, a stick circuit for saidrelay, and means including a timing device operable upon said stickcircuit for opening it a predetermined interval of time after theenergization of said relay and thereby causing a reversal in thedirection of operation of said platen.

11. In a hydraulic press system, a platen, rams operating said platen inopposite directions, means includingcontinuou'sly operating pumpingmeans connected to said rams for delivering operating fluid to said ramsalternately, and thus operating said platen in alternate directions, asource of operating fluid, connections from said source to both rams,valve means in said connections, a relay and its circuit, meanscontrolled by said relay for changing the delivery of said pumping meansfrom one ram to the other, means also controlled by said relay forchanging said valve means concurrently with the change in said pumpingmeans, switch means for closing said relay circuit to initiate anoperation of said platen in one direction, a stick circuit for saidrelay, means including a timing device operable upon saidstickcircuitfor opening it a predetermined interval of time after the energizationof said relay and thereby causing a reversal in the direction ofoperationof said platen, and means to operate said valve means whilesaid relay remains unchanged and separately from said means for changingthe direction of delivery of said pumping means.

12. In a hydraulic press system, a platen, means for operating saidplaten in alternate directions, means controlling the direction ofoperation of said platen andincluding a relay and its circuit, switchmeans for closing the circuit of said relay to initiate an operation ofsaidplaten, a stick circuit for said relay, and means including a timingdevice controlled by said relay and having a switch in series in saidstick circuit which it opens for opening said stick circuit apredetermined length of time after said stick circuit is closed, wherebythe relay will be deenergized and travel of the platen in one directionstopped.

13. In a hydraulic press system a platen, means for operating saidplaten in alternate directions,

means controlling the direction of operation of said platen andincluding a relay and its circuit, switch means for closing the circuitof said relay to initiate an operation of said platen, a stick circuitfor said relay, a time limit relay operable to open said stick circuit apredetermined length of time after being set in operation, a circult forsaid time limit relay in turn controlled by the first relay, so that thetime limit relay will be automatically set in operation upon the ineither direction under pressure so as to cause operation of said platenin either direction; motor means for changing the delivery of said pumpfrom one ram to the other, motor means for forcibly operating said valvefrom one position to another, means including a common control elementfor causing operation of both of said motor means at substantially, thesame time, the control of both of said motor means causing thepositioning of said valve to connect said source to said main ram whensaid pump is delivering fluid to said pull back ram, and means foradditionally causing an operation of the second of said motor meansduring a pressing movement of said platen to position said valve toconnect said source to said main ram while the first motor means is in aposition to cause delivery of fluid by said pumping means to said mainram, whereby said platen may be held in any position.

15. In a hydraulic press system, a platen, hydraulic means for movingsaid platen in alternate directions to and from pressing position, meansincluding a relay operable on said means for controlling the directionof travel of said platen, a regular circuit for said relay which whenclosed will energize said relay and initiate a forward movement of saidplaten, a stick circuit for holding said relay energized, means for'opening said stick circuit to terminate said forward movement of theplaten and cause a reverse movement of the platen, and means includingan electric circuit and a switch therein but operated by said platenduring a return movement of said platen for closing said relay regularcircuit and causing a reversal of travel of said platen and initiateanother forward movement of the platen a predetermined and substantiallength of time after operation of said switch by said platen.

16. In a hydraulic press system, a main ram, a pull back ram, a platenoperated by said rams in alternate directions, a source of operatingfluid, pumping means, connections between said rams, said source andsaid means by which fluid may be delivered under pressure to said ramsselec tively, electrical means for controlling the delivery of operatingfluid to one ram or the other and including a controlling circuit,timing means free of control by the pressure on said platen and set inoperation automatically by said electrical means when said electricalmeans is operated to initiate a pressing movement of said platen, and

operable to cause a return movement of said platen a predeterminedlength of time after the pressing movement of said platen is initiated,and switch means for said circuit, operable by said platen at the end ofits return movement for causing automatically a reversal of the platenand its start on a forward movement.

17. In a hydraulic press system, a platen, hydraulic means for operatingsaid platen in alternate directions, means for controlling the directionof operation of said platen, and means exclusive of said hydraulic meansand operable by said platen during a return movement for changing saidcontrolling means to initiate a forward movement of saidplatenautomatically after the lapse of an appreciable length of timefollowing completion of the return movement of said platen, said lastnamed means including a control element adjustable into differentselected positions along the path of travel of said platen.

18. In a hydraulic press system, a platen, hydraulio. means foroperating said platen in alternate directions, means for controlling thedi-- rection of operation of said platen selectively,

means operating said controlling means to reverse the direction ofoperation of said platen and I said platen, and a timing device,exclusive of said hydraulic means, set in operation by the platen atapproximately the completion of a return movement for operating saidcontrolling means to cause a forward movement thereof a predeterminedand substantialinterval of time after said platen substantiallycompleted its return movement.

19. In a hydraulic press system, a platen, hy-

draulic means including a continuously operating reversible pump, foroperating said platen in alternate directions by hydraulic pressure fromsaid pump, means for reversing said pump to control the direction ofoperation of said .platen selectively, and timing means set intooperation automatically by said platen at an intermediate point in itsmovement in one direction for operating said controlling means toreverse the delivery of said pump and thereby the direction of operationof said platen, a predetermined interval of time thereafter. I

20.'In a hydraulic press system, a platen, a main ram and a pull backram connected to said platen for operating it in alternate directions, areversible, variable delivery pump, pipes connecting said pump to saidrams for transferring fluid between the rams alternately upon reversalof the direction of delivery of the pump to control the direction oftravel .of said platen, a pheck valve in the pipe connecting said pumpto the pull back ram, opening to pass fluid from, the pump to that ramand closing automatically to prevent reverse flow, a source of fluid,pipes connecting said source to each of said rams and to-that side ofthe pump which is connected.

through said check valve to the pull back ram, and valves in the lastmentioned pipes operable to prevent escape of fluid from the pull backram and by-pass fluid delivered by the pump towards the main ram, backto said source and pump, for

stopping and holding said platen in any intermediate position during itspressing movement with the pump delivering at approximately the samerate and in the same direction.

21. In a hydraulic press system, a platen, rams connected to said platenfor operating it in alternate directions, a continuously operating pump,connections from said pump to said rams, a source of fluid, a conduitfrom said source to each ram,-a differential valve having two valveelements connected in parallel in said conduits and effective when opento pass fluid from said source to said rams, fluid actuated meansoperating outside of said valve elements for forcibly operating saiddifferential valve elements and for changing the delivery of fluid fromsaid pump to one ram or the other depending upon which ram is to beoperated, electrical means for controlling said fluid actuated means tocause forcible operation of said differential valve and to alter thedirection of transfer of fluid from one ram to the other in apredetermined relation to one another that will cause operation of saidplaten in alternate directions, and means also controlling said fluidactuated means for effecting forcible operation of said differentialvalve out of said predetermined relation while continuing the deliveryof fluid to one of said rams, whereby said platen may be selectivelystopped and held in any intermediate position while travelling in onedirection, and travel in the same direction resumed when desired.

22. In a hydraulic press system, a platen, a main ram connected to saidplaten for operating it in a pressing direction, a pull-back.ram forretracting the platen, a continuously operating pump connected to saidrams for transferring fluid in either direction between them todetermine the direction of operation of said platen, a reservoir, adifferential .valve having two valve elements connected between saidreservoir and said rams, a motor for forcibly operating saiddifferential valve elements and connecting said reservoir alternately tosaid rams, means including another motor for changing the delivery offluid from said pump from one ram to the other, means including anelectrical circuit for operating said motors in a desired relation toone another and for causing travel of said platen in alternatedirections, and means for additionally controlling the motor of thedifferential valve and operating said valve elements to closecommunication between said pull-back ram and reservoir and to opencommunication between said main ram and reservoir while said pump isdelivering fluid to said main ram, whereby said platen may be stoppedand held in any selected point in its travel in a pressing directionwhile said pump is delivering fluid to said main ram.

23. In a hydraulic press system, a platen, a main ram for operating saidplaten in a pressing direction, a pull-back ram for retracting saidplaten, a reversible delivery pump connected to said rams fortransferring fluid between them in either direction, a check valve inthe connection from said pump to the'pull-back ram for restrict! ingflow therethrough toward said pull-back ram, a reservoir, branchconnections therefrom to said rams, a differential valve having twovalve elements, one in each of said branch connections for connectingsaid reservoir alternately to said rams, a pipe connecting saidreservoir to said pump at the side connected to said pull-back ram andbetween the pump and the check valve,

a free check valve in the pipe between said reservoir and pump andrestricting flow therethrough to a direction toward said pump, means forreversing the pump to cause operation of said platen in alternatedirections, and means for forcibly operating said differential valveelements to close communication betweensaid pull-back ram and reservoirwhile said pump continues to deliver fluid to said main ram whereby saidplaten may be stopped and held in any intermediate position in apressing movement, and resumption of a pressing movement selectivelyobtained by a return of the differential valve elements to the positionsin which the valve elements connect the reservoir to said pull-back .ramand close communication between said main ram and reservoir.

'24. In a hydraulic press system, a platen, a main ram for operatingsaid platen in a pressing direction, a pull-back ram for retracting saidplaten, a reversible delivery pump connected to said rams fortransferring fluid between them in either direction, a check valve inthe connection from said pump to the pull-back ram for restricting flowtherethrough toward said pull-back ram, a reservoir, branch connectionstherefrom to said rams, a differential valve having two valve eleandbetween the pump and the check valve, a free check valve in the pipebetween said reservoir and pump and restricting flow therethrough to adirection toward said pump, means for reversing the pump to causeoperation of said platen in alternate directions, means for forciblyoperating said difierential valve elements to close communicationbetween said pull-back ram and reservoir while said pump continues todeliver fluid to said main ram whereby said platen may be stopped andheld in any intermediate position in a pressing movement, and resumptionof a pressing movement selectively obtained by a return of thedifierential valve elements to the positions in which the difierentialvalve connects the reservoir to said pull-back ram and closescommunication between said main ram and reservoir, and means operated bysaid platen during a retraction movement for forcibly opening the freecheck valveand stopping the retraction of said platen while said pump isdelivering said fluid toward said pull-back ram.

25. In a hydraulic press system. a platen, a main ram for operating saidplaten in a pressing direction, a pull-back ram for retracting saidplaten, a reversible delivery pump connected to said rams fortransferring fluid between them in either direction, a check valve inthe connection from said pump to the pull-back ram for restricting flowtherethrough toward said pull-back ram, a reservoir, branch connections,therefrom to said rams, a differential valve having two valve elements,one in each of said branch connections, for connecting said reservoiralternately to said rams, a pipe connecting said reservoir to said pumpat the side connected to said pull-back ram and between the pump and thecheck valve, a free check valve in the pipe between said reservoir andpump and restricting flow therethrough to a direction toward said pump,means for reversing the pump to cause operation of said platen inalternate directions, means for forcibly operating said diiierentialvalve elements to close communication between said pull-back ram andreservoir while said pump continues to deliver fluid to said main ramwhereby said platen may be stopped and held in any intermediate positionin a pressing movement, and resumption of a pressing movementselectively obtained by a return of the differential valve elements tothe positions in which they connect the reservoir to said pull-back ramand close communication between said main ram and reservoir, meansoperated by said platen during a retraction movement for forciblyopening the free check valve and stopping the retraction of said platenwhile said pump is delivering said fluid toward said pullback ram, andelectrical means for controlling the direction of delivery of said pumpand of the forcible operation of said differential valve elements tocontrol the direction of travel of said platen, said electrical meansbeing operable by said platen during a retraction movement thereof forautomatically reversing the delivery of said pump and forcibly operatingsaid differential valve to automatically initiate a pressing operationof said platen after a desired return movement of the platen.

26. In a hydraulic press system, a platen, a main ram for operating saidplaten in aapressing direction, a pull-back ram for retracting saidvplaten, a reversible delivery pump connected to 'said rams fortransferring fluid between them in either direction, a check valve inthe connection from said pump to the pull-back ram for restricting flowtherethrough toward said pull-back ram, a reservoir, branch connectionstherefrom to said rams, a differential valve having two valve elements,one in each of said branch connections for connecting said reservoiralternately to said rams, a pipe connecting said reservoir to said pumpat the side connected to said pull-back ram and between the pump and thecheck valve, a free check valve in the pipe between said reservoir andpump and restricting flow therethrough to a direction toward said pump,means for reversing the pump to cause operation of said platen inalternate directions, means for forcibly operating said differentialvalve elements to close communication between said pull-back ram andreservoir while said pump continues to deliver fluid to said main ramwhereby said platen may be stopped and held in any intermediate positionin a pressing movement; and resumption of a pressing movementselectively obtained by a return of the differential valve elements tothe position in which they connect the reservoir to said pull-back ramand close communication between said main ram and reservoir, meansoperated by said platen during a retraction movement for forciblyopening the check valve in said pipe connecting said reservoir to saidpump and stopping the retraction of 'said platen while said pump isdelivering said fluid toward said pull-back ram, electrical means forcontrolling the direction of delivery of said pump and of the forcibleoperation of said differential valve elements to control the directionof travel of said platen, said electrical means being operable by saidplaten during a retraction movement thereof for automatically reversingthe delivery of said pump andrections, means including a stick relay andits circuit for controlling said operating means and having a closedcircuit condition for said relay when operation of said platen in onedirection is desired, switch means connected in the circuit of saidrelay for energizing said relay to initiate a movement of the platen inone direction, a timing device for opening said stick circuit andcausing a reversal of the direction of travel of said platen, meansoperated by said platen during its travel ina pressing direction forrendering said timing device active, whereby 'said stick circuit will beopened a predetermined interval of time after the timing device isrendered active, and means for incapacitating said platen operateddevice

